Brown Eyes Are More Trustworthy, But Why?

Ever wonder what makes you feel that instinctive sense of trust — or mistrust — when you meet someone new? In a new study published this week in the online journal PLoS ONE, researchers at Charles University in the Czech Republic explored this question by asking 238 participants to look at the faces of 80 students and rate their trustworthiness, attractiveness and dominance.

As expected, the team found that all three of these characteristics aligned pretty well with each other. Faces that they perceived as trustworthy also seemed more attractive and dominant, and vice versa. On the whole, the participants also tended to find female faces more trustworthy than their male counterparts.

But the researchers also stumbled upon a somewhat unexpected correlation — people tended to view brown eyes as more trustworthy than blue eyes regardless of whether the person doing the rating was a man or woman with blue eyes or brown eyes.

Additionally, even when the researchers adjusted the numbers to account for attractiveness and dominance, the same pattern held: brown-eyed faces were rated as more trustworthy than blue-eyed faces. Although this preference was stronger in some participants than in others, all of test subjects tended to find brown eyes more dependable.

This clear bias towards brown eyes initially left the researchers scratching their heads.

In an attempt to get to the bottom of the mystery, the scientists used a computer program to modify the eye colors of the faces in the images, simply flip-flopping the brown eyes for blue and the blue eyes for brown. Other facial features were left untouched.

After running the same tests again, the team made yet another bizarre discovery. Changing the eye color did not change how the participants rated the faces. The formerly brown-eyed faces that had been changed to blue were still rated as more trustworthy, while the faces that had their blue eyes swapped for brown were still perceived as suspect. Apparently, it wasn´t eye color alone that was affecting how the subjects perceived trustworthiness.

Hot on the trail of a rational explanation for their bizarre findings, the research team decided to analyze the shape and structure of the faces in the images. By generating a grid-like representation of each face and measuring 72 distinct facial “landmarks”, they began to notice a pattern: brown eyes were connected to a different general set of facial features than blue eyes.

So what kinds of facial features were linked with the two different eye colors? For men, brown eyes tended to accompany larger mouths, broader chins, bigger noses and more prominent eyebrows. Blue-eyed men, on the other hand, generally had more angular and prominent lower faces, smaller eyes, longer chins, thinner mouths with corners that point downward, and eyebrows that are farther apart. Not surprisingly, the features that indicate trustworthiness are closely related to the facial expressions that people make when they are happy and may help to explain why those brown-eye-linked features are easily associated with reliability.

When the researchers turned to examine the structure of the female faces, however, they stumbled upon yet another oddity: Although the same correlation between eye color and trustworthiness had been observed for the photographs of women´s faces, the researchers did not find the same correlation between eye color facial features as they had in men. In fact, women´s faces in general tended to have a far fewer variations in their features compared to men´s faces.

While they already have a few working theories about why this might be the case, the team says that further research is needed to understand the connection between eye color and trustworthiness in women´s faces.

The capacity for intimate social interactions and trusting relationships were critical to the evolutionary survival of humans. So why would some humans develop inherently ℠untrustworthy´ facial features when these pose a clear disadvantage to survival? How is eye color linked with various facial features at the genetic level, and when did these genetic developments appear in our evolutionary history? To what degree are these facial features the direct result of genes versus environmental factors during an individual´s development?

Like many scientific advances, it appears that this study has — at least initially — created more questions than it has answered.